COMBUSTION FLUE GAS NOx TREATMENT

Abstract

Combustion flue gas containing NOX and SOX is treated to remove NOX in a multistep system in which NOX is reduced in the flue gas stream via selective catalytic reduction or selective non-catalytic reduction with ammonia or an ammonia-forming compound, followed treatment with hydrogen peroxide to remove residual ammonia and, optionally, treatment with an alkali reagent to reduce residual NOX in the flue gas stream. The NOX-depleted flue gas stream may also be subjected to a desulfurization treatment for removal of SOX.

Description

FIELD OF THE INVENTION[0001]The present invention relates to air pollution control and more particularly to the treatment of a combustion flue gas stream from a stationary source to remove its NOX contaminants before the gas stream is released into the atmosphere.BACKGROUND OF THE INVENTION[0002]Combustion of fuels such as coal, coke, natural gas or oil typically results in the presence of pollutants in the combustion flue gas stream resulting from the combustion process or derived from impurities present in the fuel source. Electric utility power plants that burn coal are a significant source of such combustion process air pollutants, but other stationary fuel-burning facilities such as industrial boilers, waste incinerators, and manufacturing plants are also pollution sources.[0003]The primary air pollutants formed by these stationary high temperature combustion sources are sulfur oxides (e.g., SO2 and SO3), also called SOX gases, and nitrogen oxides, also called NOX gases, both o...

AI Technical Summary

Benefits of technology

[0017]Another embodiment of the present invention is a method for removing NOX from a flue gas stream comprising injecting ammonia or an ammonia-forming compound into a combustion flue gas stream containing NOx, wherein an excess of ammonia is introduced into the flue gas stream as an agent for reducing the NOx, to yield a flue gas stream containing unreacted residual ammonia and a reduced concentration of NOx; thereafter injecting hydrogen pero

Problems solved by technology

Combustion of fuels such as coal, coke, natural gas or oil typically results in the presence of pollutants in the combustion flue gas stream resulting from the combustion process or derived from impurities present in the fuel source.

Electric utility power plants that burn coal are a significant source of such combustion process air pollutants, but other stationary fuel-burning facilities such as industrial boilers, waste incinerators, and manufacturing plants are also pollution sources.

Such integrated air pollution control systems represent a particular challenge in situations requiring retrofitting of first-time or additional or enhanced pollution control measures, e.g., older coal-fired electric power plants without any desulfurization measures or power plants with SOX controls requiring modifications for control of NOX gas emissions.

The presence of NOX in a flue gas stream discharged to the atmosphere can result in a “brown plume” and is a contributor to ground-level ozone pollution (“smog”) and to acidifying nitrate deposition.

The wet scrubbing desulfurization techniques utilized for SOX removal from combustion flue gas are largely unsuccessful for removal of NO that is also present since the latter has low water solubility and is not amenable to aqueous alkali desulfurization scrubbing techniques.

A drawback to commercial SNCR systems is their NOX removal rates of only 30-70%.

In actual commercial practice, the engineering challenge is the design of an integrated air pollution control system that can be retrofitted to existing fossil-fuel fired electric utility plants that are in need of updated or upgraded pollution controls for one or more of SO2, SO3, NO, NO2, Hg, HCl, HF, CO2 and particulates.

Images